1. Field of the Invention
This invention relates to a nonvolatile magnetic memory and a nonvolatile magnetic memory array which are preferably usable as a magnetic random access memory (MRAM). Also, this invention relates to a method for fabricating the nonvolatile magnetic memory. Moreover, this invention relates to a method for recording in the nonvolatile magnetic memory and a method for reading out from the nonvolatile magnetic memory.
2. Description of the Prior Art
Various electronic devices have been employed under a specific condition such as an aero-space, and thus, it is desired to establish a recording device where once stored information can not be deleted by the irradiation of a radioactive ray. In this point of view, large radioactive-resistance and nonvolatile MRAMs having their respective simply structured magnetic memory cells are researched and developed.
Conventionally, such a magnetic memory cell is shaped rectangular, and information “0” or “1” is stored on the magnetic direction of the magnetic memory cell. With the conventional magnetic memory cell, however, the magnetic flux originated from the magnetization is leaked outside from the magnetic memory cell due to the configuration thereof. In order to increase the recording capacity of the MRAM, in contrast, such an attempt is made as to arrange a plurality of magnetic memory cells in high density. In this case, however, the leaked magnetic flux affects significantly on the adjacent magnetic memory cells, and thus, the intended high density MRAM can not be realized.
In this point of view, the inventors have developed a ring-shaped magnetic memory where a right handed (clockwise) magnetization or a left-handed (anticlockwise) magnetization is created in vortex, and information “0” or “1” is stored on the rotative direction of the magnetization thereof (Japanese Patent application 2002-73681).
In this case, since a magnetic flux is not leaked from the magnetic memory, if a plurality of magnetic memory are arranged in high density as mentioned above, the leaked magnetic flux can not almost affect on the adjacent magnetic memories, so that a high density MRAM can be realized.
With the ring-shaped magnetic memory, however, the motion of the magnetic domain wall is prevented due to the inside external wall, so that the magnetization can not be easily inverted. In order to control the right handed magnetization and the left handed magnetization, it is required to flow current perpendicular to the ring-shaped magnetic memory and thus, to generate rotative magnetic field in the magnetic memory along the ring-shaped configuration, as indicated in “Journal of Applied Physics, 87, 9, p6668-6673(2001)”. Therefore, the control of the magnetic condition of the ring-shaped magnetic memory is very difficult and complicated, so that the ring-shaped magnetic memory can not be practically employed.